A longitudinal study of Babesia microti infection in seropositive blood donors

Human Babesia odocoilei and Bartonella spp. co-infections in the Americas

BACKGROUND

In recent years, Babesia and Bartonella species co-infections in patients with chronic, nonspecific illnesses have continued to challenge and change the collective medical understanding of "individual pathogen" vector-borne infectious disease dynamics, pathogenesis and epidemiology. The objective of this case series is to provide additional molecular documentation of Babesia odocoilei infection in humans in the Americas and to emphasize the potential for co-infection with a Bartonella species.

METHODS

The development of improved and more sensitive molecular diagnostic techniques, as confirmatory methods to assess active infection, has provided increasing clarity to the healthcare community.

RESULTS

Using a combination of different molecular diagnostic approaches, infection with Babesia odocoilei was confirmed in seven people suffering chronic non-specific symptoms, of whom six were co-infected with one or more Bartonella species.

CONCLUSIONS

We conclude that infection with Babesia odocoilei is more frequent than previously documented and can occur in association with co-infection with Bartonella spp.

Specific and Sensitive Diagnosis of Babesia microti Active Infection Using Monoclonal Antibodies to the Immunodominant Antigen BmGPI12

The apicomplexan pathogen Babesia microti is responsible for most cases of human babesiosis worldwide. The disease, which presents as a malaria-like illness, is potentially fatal in immunocompromised or elderly patients, making the need for its accurate and early diagnosis an urgent public health concern. B. microti is transmitted primarily by Ixodes ticks but can also be transmitted via blood transfusion. The parasite completes its asexual reproduction in the host red blood cell, where each invading merozoite develops and multiplies to produce four daughter parasites. While various techniques, such as microscopy, PCR, and indirect fluorescence, have been used over the years for babesiosis diagnosis, detection of the secreted B. microti immunodominant antigen BmGPI12 using specific polyclonal antibodies was found to be the most effective method for the diagnosis of active infection and for evaluation of clearance following drug treatment. Here, we report the development of a panel of 16 monoclonal antibodies against BmGPI12. These antibodies detected secreted BmGPI12 in the plasma of infected humans. Antigen capture assays identified a combination of two monoclonal antibodies, 4C8 and 1E11, as a basis for a monoclonal antibody-based BmGPI12 capture assay (mGPAC) to detect active B. microti infection. Using a collection of 105 previously characterized human plasma samples, the mGPAC assay showed 97.1% correlation with RNA-based PCR (transcription-mediated amplification [TMA]) for positive and negative samples. The mGPAC assay also detected BmGPI12 in the plasma of six babesiosis patients at the time of diagnosis but not in three matched posttreatment samples. The mGPAC assay could thus be used alone or in combination with other assays for accurate detection of active B. microti infection.

Technologies for Detection of Babesia microti: Advances and Challenges

The biology of intraerythrocytic Babesia parasites presents unique challenges for the diagnosis of human babesiosis. Antibody-based assays are highly sensitive but fail to detect early stage Babesia infections prior to seroconversion (window period) and cannot distinguish between an active infection and a previously resolved infection. On the other hand, nucleic acid-based tests (NAT) may lack the sensitivity to detect window cases when parasite burden is below detection limits and asymptomatic low-grade infections. Recent technological advances have improved the sensitivity, specificity and high throughput of NAT and the antibody-based detection of Babesia. Some of these advances include genomics approaches for the identification of novel high-copy-number targets for NAT and immunodominant antigens for superior antigen and antibody-based assays for Babesia. Future advances would also rely on next generation sequencing and CRISPR technology to improve Babesia detection. This review article will discuss the historical perspective and current status of technologies for the detection of Babesia microti, the most common Babesia species causing human babesiosis in the United States, and their implications for early diagnosis of acute babesiosis, blood safety and surveillance studies to monitor areas of expansion and emergence and spread of Babesia species and their genetic variants in the United States and globally.

Development of a Multiplex Droplet Digital PCR Assay for the Detection of Babesia, Bartonella, and Borrelia Species

We describe the development, optimization, and validation of a multiplex droplet digital PCR (ddPCR) assay for the simultaneous detection of Babesia, Bartonella, and Borrelia spp. DNA from several sample matrices, including clinical blood samples from animals and humans, vectors, in-vitro infected human and animal cell lines, and tissues obtained from animal models (infected with Bartonella and/or B. burgdorferi). The multiplex ddPCR assay was able to detect 31 Bartonella, 13 Borrelia, and 24 Babesia species, including Theileria equi, T. cervi, and Cytauxzoon felis. No amplification of Treponema or Leptospira spp. was observed. Sensitivity of 0.2-5 genome equivalent DNA copies per microliter was achieved for different members of the Bartonella and Borrelia genus, depending on the species or matrix type (water or spiked blood DNA) tested. The ddPCR assay facilitated the simultaneous detection of co-infections with two and three vector-borne pathogens comprising four different genera (Babesia, Bartonella, Borrelia, and Theileria) from clinical and other sample sources.

Development of a Multiplex Bead Assay To Detect Immunoglobulin G Antibodies to Babesia duncani in Human Serum

Babesia duncani is the causative agent of babesiosis in the western United States. The indirect fluorescent antibody (IFA) assay is the diagnostic test of choice for detection of B. duncani-specific antibodies. However, this test requires parasitized red blood cells harvested from infected hamsters, and test results are often difficult to interpret. To simplify serological testing for B. duncani, a proteomics approach was employed to identify candidate immunodiagnostic antigens. Several proteins were identified by electrospray ionization mass spectrometric analysis, and four recombinant protein constructs were expressed and used in a multiplex bead assay (MBA) to detect B. duncani-specific antibodies. Two antigens, AAY83295.1 and AAY83296.1, performed well with high sensitivities and specificities. AAY83295.1 had a higher sensitivity (100%) but lower specificity (89%) than AAY83296.1, which had a sensitivity of 90% and a specificity of 96%. Combining these two antigens did not improve the performance of the assay. This MBA could be useful for diagnosis, serosurveillance, and blood donor screening for B. duncani infection.

Babesia microti: Pathogen Genomics, Genetic Variability, Immunodominant Antigens, and Pathogenesis

More than 100 Babesia spp. tick-borne parasites are known to infect mammalian and avian hosts. Babesia belong to Order Piroplasmid ranked in the Phylum Apicomplexa. Recent phylogenetic studies have revealed that of the three genera that constitute Piroplasmida, Babesia and Theileria are polyphyletic while Cytauxzoon is nested within a clade of Theileria. Several Babesia spp. and sub-types have been found to cause human disease. Babesia microti, the most common species that infects humans, is endemic in the Northeastern and upper Midwestern United States and is sporadically reported elsewhere in the world. Most infections are transmitted by Ixodid (hard-bodied) ticks, although they occasionally can be spread through blood transfusion and rarely via perinatal transmission and organ transplantation. Babesiosis most often presents as a mild to moderate disease, however infection severity ranges from asymptomatic to lethal. Diagnosis is usually confirmed by blood smear or polymerase chain reaction (PCR). Treatment consists of atovaquone and azithromycin or clindamycin and quinine and usually is effective but may be problematic in immunocompromised hosts. There is no human Babesia vaccine. B. microti genomics studies have only recently been initiated, however they already have yielded important new insights regarding the pathogen, population structure, and pathogenesis. Continued genomic research holds great promise for improving the diagnosis, management, and prevention of human babesiosis, and in particular, the identification of lineage-specific families of cell-surface proteins with potential roles in cytoadherence, immune evasion and pathogenesis.

Preventing Transfusion-Transmitted Babesiosis

Babesia are tick-borne intra-erythrocytic parasites and the causative agents of babesiosis. Babesia, which are readily transfusion transmissible, gained recognition as a major risk to the blood supply, particularly in the United States (US), where Babesia microti is endemic. Many of those infected with Babesia remain asymptomatic and parasitemia may persist for months or even years following infection, such that seemingly healthy blood donors are unaware of their infection. By contrast, transfusion recipients are at high risk of severe babesiosis, accounting for the high morbidity and mortality (~19%) observed in transfusion-transmitted babesiosis (TTB). An increase in cases of tick-borne babesiosis and TTB prompted over a decade-long investment in blood donor surveillance, research, and assay development to quantify and contend with TTB. This culminated in the adoption of regional blood donor testing in the US. We describe the evolution of the response to TTB in the US and offer some insight into the risk of TTB in other countries. Not only has this response advanced blood safety, it has accelerated the development of novel serological and molecular assays that may be applied broadly, affording insight into the global epidemiology and immunopathogenesis of human babesiosis.

Eastern Equine Encephalitis Virus: A Scoping Review of the Global Evidence

Background: Eastern equine encephalitis virus (EEEV) is a mosquito-borne virus that is primarily found in North America and the Caribbean. Over the past decade there has been an increase in virus activity, including large outbreaks in human and horse populations. Predicted climate change is expected to affect the range of mosquitoes including vectors of EEEV, which may alter disease risk posing a public health concern. Methods: A scoping review (ScR) was conducted to identify and characterize the global evidence on EEEV. A thorough search was conducted in relevant bibliographic databases and government websites. Two reviewers screened titles and abstracts for relevance and the characteristics of relevant articles were extracted using a uniformly implemented data collection form. The study protocol was developed a priori and described the methods and tools used and this article follows the PRISMA-ScR guidelines for reporting ScRs. Results: The ScR included 718 relevant research articles. The majority of the articles originated from North America (97%) between 1933 and 2019. EEEV has been identified in 35 species of mosquitoes, over 200 species of birds, various domestic animals, wild mammals, reptiles, and amphibians. Articles identified in this ScR primarily covered three topic areas: epidemiology of hosts and vectors (344 articles) including surveillance results (138), pathogenesis of EEEV in hosts (193), and in vitro studies characterizing EEEV (111). Fewer articles evaluated the accuracy of diagnostic tests (63), the efficacy of mitigation strategies (62), transmission dynamics (56), treatment of EEEV in hosts (10), societal knowledge, attitudes, and perceptions (4), and economic burden (2). Conclusion: With the projected impact of climate change on mosquito populations, it is expected that the risk of EEEV could change resulting in higher disease burden or spread into previously unaffected areas. Future research efforts should focus on closing some of the important knowledge gaps identified in this ScR.

Clinical Practice Guidelines by the Infectious Diseases Society of America (IDSA): 2020 Guideline on Diagnosis and Management of Babesiosis

The purpose of this guideline is to provide evidence-based guidance for the most effective strategies for the diagnosis and management of babesiosis. The diagnosis and treatment of co-infection with babesiosis and Lyme disease will be addressed in a separate Infectious Diseases Society of America (IDSA), American Academy of Neurology (AAN), and American College of Rheumatology (ACR) guideline [1]. Recommendations for the diagnosis and treatment of human granulocytic anaplasmosis can be found in the recent rickettsial disease guideline developed by the Centers for Disease Control and Prevention [2]. The target audience for the babesiosis guideline includes primary care physicians and specialists caring for this condition, such as infectious diseases specialists, emergency physicians, intensivists, internists, pediatricians, hematologists, and transfusion medicine specialists.

Human babesiosis: recent advances and future challenges

PURPOSE OF REVIEW

As human babesiosis caused by apicomplexan parasites of the Babesia genus is associated with transfusion-transmitted illness and relapsing disease in immunosuppressed populations, it is important to report novel findings relating to parasite biology that may be responsible for such pathology. Blood screening tools recently licensed by the FDA are also described to allow understanding of their impact on keeping the blood supply well tolerated.

RECENT FINDINGS

Reports of tick-borne cases within new geographical regions such as the Pacific Northwest of the USA, through Eastern Europe and into China are also on the rise. Novel features of the parasite lifecycle that underlie the basis of parasite persistence have recently been characterized. These merit consideration in deployment of both detection, treatment and mitigation tools such as pathogen inactivation technology. The impact of new blood donor screening tests in reducing transfusion transmitted babesiosis is discussed.

SUMMARY

New Babesia species have been identified globally, suggesting that the epidemiology of this disease is rapidly changing, making it clear that human babesiosis is a serious public health concern that requires close monitoring and effective intervention measures. Unlike other erythrocytic parasites, Babesia exploits unconventional lifecycle strategies that permit host cycles of different lengths to ensure survival in hostile environments. With the licensure of new blood screening tests, incidence of transfusion transmission babesiosis has decreased.

Transfusion transmitted babesiosis: A systematic review of reported cases

BACKGROUND

Transfusion transmitted babesiosis (TTB) has a high mortality rate but may go unrecognized, particularly in non-endemic areas. We therefore conducted a systematic review to better characterize clinical aspects of TTB.

METHODS

A literature search was conducted in PubMed and CINAHL databases, from which 25 eligible articles describing 60 TTB patients met criteria for data extraction.

RESULTS

Symptom evaluation was provided for 25 implicated donors: 18/25 (72%) were asymptomatic while 7/25 (28%) had mild flu-like symptoms but were asymptomatic at time of donation. It was common for a single donor or donation to infect multiple patients. Where reported, species included B. microti - 54/60 (90%), B. duncani - 3/60 (5%), and B. divergens-like/MO-1 - 1/60 (2%). Most TTB patients (44/60, 73%) resided in endemic states, while most TTB deaths 6/9 (67%) occurred in non-endemic states. Severity of hemolysis was proportional to degree of parasitemia. Mortality in our series was 9/60 (15%); most deaths occurred at extremes of the age spectrum: 6/9 non-survivors were aged >55 years, 2/9 were <1 year, only 1/9 was 2-54 years. Number of comorbidities was higher among non-survivors (median = 4) compared to survivors (median = 1).

CONCLUSIONS

All implicated donors (for which symptoms data were reported) resulting in TTB infections were asymptomatic at the time of donation, and it was common for a single donor or donation to infect multiple patients. Mortality of TTB appeared highest among those with more comorbidities and in non-endemic states. Heightened awareness of this diagnosis is key in its recognition.

Persistence of Babesia microti Infection in Humans

Persistent infection is a characteristic feature of babesiosis, a worldwide, emerging tick-borne disease caused by members of the genus Babesia. Persistence of Babesia infection in reservoir hosts increases the probability of survival and transmission of these pathogens. Laboratory tools to detect Babesia in red blood cells include microscopic detection using peripheral blood smears, nucleic acid detection (polymerase chain reaction and transcription mediated amplification), antigen detection, and antibody detection. Babesia microti, the major cause of human babesiosis, can asymptomatically infect immunocompetent individuals for up to two years. Chronically infected blood donors may transmit the pathogen to another person through blood transfusion. Transfusion-transmitted babesiosis causes severe complications and death in about a fifth of cases. Immunocompromised patients, including those with asplenia, HIV/AIDS, malignancy, or on immunosuppressive drugs, often experience severe disease that may relapse up to two years later despite anti-Babesia therapy. Persistent Babesia infection is promoted by Babesia immune evasive strategies and impaired host immune mechanisms. The health burden of persistent and recrudescent babesiosis can be minimized by development of novel therapeutic measures, such as new anti-parasitic drugs or drug combinations, improved anti-parasitic drug duration strategies, or immunoglobulin preparations; and novel preventive approaches, including early detection methods, tick-avoidance, and blood donor screening.

Human babesiosis

Babesiosis is a worldwide emerging tick-borne disease that is increasing in frequency and geographic range. It imposes a significant health burden, especially on those who are immunocompromised and those who acquire the infection through blood transfusion. Death from babesiosis occurs in up to 20 percent of these groups. Diagnosis is confirmed with identification of typical intraerythrocytic parasites on a thin blood smear or Babesia DNA using PCR. Treatment consists of atovaquone and azithromycin or clindamycin and quinine, and exchange transfusion in severe cases. Personal and communal protective measures can limit the burden of infection but it is important to recognize that none of these measures are likely to prevent the continued expansion of Babesia into non-endemic areas.

Performance Evaluation of a Prototype Architect Antibody Assay for Babesia microti

The tick-borne protozoan Babesia microti is responsible for more than 200 cases of transfusion-transmitted babesiosis (TTB) infection in the United States that have occurred over the last 30 years. Measures to mitigate the risk of TTB include nucleic acid testing (NAT) and B. microti antibody testing. A fully automated prototype B. microti antibody test was developed on the Architect instrument. The specificity was determined to be 99.98% in volunteer blood donors (n = 28,740) from areas considered to have low endemicity for B. microti The sensitivity of the prototype test was studied in experimentally infected macaques; a total of 128 samples were detected as positive whereas 125 were detected as positive with an indirect fluorescent antibody (IFA) test; additionally, 83 (89.2%) of the PCR-positive samples were detected in contrast to 81 (87.1%) using an IFA test. All PCR-positive samples that tested negative in the prototype antibody test were preseroconversion period samples. Following seroconversion, periods of intermittent parasitemia occurred; 17 PCR-negative samples drawn in between PCR-positive bleed dates tested positive both by the prototype test (robust reactivity) and IFA test (marginal reactivity) prior to the administration of therapeutic drugs, indicating that the PCR test failed to detect samples from persistently infected macaques. The prototype assay detected 56 of 58 (96.6%) human subjects diagnosed with clinical babesiosis by both PCR and IFA testing. Overall, the prototype anti-Babesia assay provides a highly sensitive and specific test for the diagnosis of B. microti infection. While PCR is preferred for detection of window-period parasitemia, antibody tests detect infected subjects during periods of low-level parasitemia.

Superior real-time polymerase chain reaction detection of Babesia microti parasites in whole blood utilizing high-copy BMN antigens as amplification targets

BACKGROUND

Babesiosis is a zoonotic disease transmitted to humans by the bite of infected ticks and caused by apicomplexan parasites, most commonly Babesia microti. Additionally, blood and blood products collected from asymptomatically infected blood donors may cause transfusion-transmitted infections in recipients. Highly sensitive molecular assays that detect parasite nucleic acid are needed for laboratory diagnosis and to identify and defer clinically silent but parasitemic blood donors.

STUDY DESIGN AND METHODS

Here we report the development and analytical and clinical characterization of a real-time polymerase chain reaction (RT-PCR)-based assay for the detection of B. microti genomic DNA in whole blood. We evaluate the detection of Babesia parasites using two separate targets, the traditional18S ribosomal subunit gene (Bm18S) and members of the abundant BMN family of seroreactive antigens (BmBMN).

RESULTS

Analytical sensitivity determination using a probit analysis demonstrated an analytical sensitivity of 30.9 parasites/mL for 18S amplification and 10.0 parasites/mL for BMN amplification The BMN primer set also demonstrates superior sensitivity for serial dilution panels prepared from clinically diagnosed Babesia-infected blood samples, generally detecting 10-fold more dilute nucleic acid.

CONCLUSIONS

Cumulatively, our data demonstrate that RT-PCR detection of the BMN family of seroreactive antigens reflects a sensitive and superior assay for the detection of B. microti in whole blood samples.

Transmission of Babesia microti Parasites by Solid Organ Transplantation

Infection with this parasite should be included in differential diagnosis of fever and anemia after blood transfusion or organ transplantation.

Babesia microti, an intraerythrocytic parasite, is tickborne in nature. In contrast to transmission by blood transfusion, which has been well documented, transmission associated with solid organ transplantation has not been reported. We describe parasitologically confirmed cases of babesiosis diagnosed ≈8 weeks posttransplantation in 2 recipients of renal allografts from an organ donor who was multiply transfused on the day he died from traumatic injuries. The organ donor and recipients had no identified risk factors for tickborne infection. Antibodies against B. microti parasites were not detected by serologic testing of archived pretransplant specimens. However, 1 of the organ donor’s blood donors was seropositive when tested postdonation and had risk factors for tick exposure. The organ donor probably served as a conduit of Babesia parasites from the seropositive blood donor to both kidney recipients. Babesiosis should be included in the differential diagnosis of unexplained fever and hemolytic anemia after blood transfusion or organ transplantation.

Transfusion-transmitted babesiosis: is it time to screen the blood supply?

PURPOSE OF REVIEW

This review summarizes the current status of blood screening to prevent transfusion-transmitted babesiosis (TTB).

RECENT FINDINGS

Babesia microti has recently been determined to be the most common transfusion-transmitted pathogen in the United States. Patients who acquire TTB often experience severe illness with an associated mortality rate of about 20%. Recent studies have demonstrated that laboratory screening using B. microti antibody and/or PCR assays can effectively identify infectious blood donors and that this approach may offer a cost- effective means of intervention. Pathogen inactivation methods may offer an alternative solution. None of these methods has yet been licensed by US Food and Drug Administration, however, and current efforts to prevent TTB rely on excluding blood donors who report having had babesiosis.

SUMMARY

TTB imposes a significant health burden on the United States population. Further research is needed to better inform decisions on optimal screening strategies and reentry criteria, but given the acute need and the currently available screening tools, initiation of blood donor screening to prevent TTB should be given high priority.

Across state lines: Fulminant Babesia microti infection in a liver transplant recipient

The potential for transmission of Babesia microti by blood transfusion is well recognized. Physicians may be unaware that products used for transfusion may be collected from geographically diverse regions. We describe a liver transplant recipient in South Carolina who likely acquired B. microti infection from a unit of blood collected in Minnesota.

The Impact of Emerging Infectious Diseases on Chinese Blood Safety

Emerging infectious diseases (EIDs) have always been one of the major threats to public health. Although the implementation of mandatory testing for 4 classical transfusion-transmitted infectious-human immunodeficiency virus, hepatitis B virus, hepatitis C virus, and syphilis-has reduced the transfusion risk of these pathogens, the potential threat of various EID agents and their constantly evolving variants to blood safety in China is not fully understood. This review presents 9 representative EID agents that are autochthonous and epidemic nationally or regionally in China. The epidemiologic status and distribution of these EID agents among donors and/or healthy populations are summarized. The potential risks of these EID agents to blood safety are discussed. The review also explores strategies to strengthen hemovigilance systems and studies to further evaluate the impact of EID agents on blood safety.

Serologic screening of United States blood donors for Babesia microti using an investigational enzyme immunoassay

BACKGROUND

The tick-borne pathogen Babesia microti has become recognized as the leading infectious risk associated with blood transfusion in the United States, yet no Food and Drug Administration-licensed screening tests are currently available to mitigate this risk. The aim of this study was to evaluate the performance of an investigational enzyme immunoassay (EIA) for B. microti as a screening test applied to endemic and nonendemic blood donor populations.

STUDY DESIGN AND METHODS

The study aimed to test 20,000 blood donors from areas of the United States considered endemic for B. microti and 10,000 donors from a nonendemic area with the investigational B. microti EIA. Repeat-reactive samples were retested by polymerase chain reaction (PCR), blood smear, immunofluorescent assay (IFA), and immunoblot assay. In parallel, serum samples from symptomatic patients with confirmed babesiosis were tested by EIA, IFA, and immunoblot assays.

RESULTS

A total of 38 of 13,757 (0.28%) of the donors from New York, 7 of 4583 (0.15%) from Minnesota, and 11 of 8363 (0.13%) from New Mexico were found repeat reactive by EIA. Nine of the 56 EIA repeat-reactive donors (eight from New York and one from Minnesota) were positive by PCR. The specificity of the assay in a nonendemic population was 99.93%. Among IFA-positive clinical babesiosis patients, the sensitivity of the assay was 91.1%.

CONCLUSION

The B. microti EIA detected PCR-positive, potentially infectious blood donors in an endemic population and exhibited high specificity among uninfected and unexposed individuals. The EIA promises to provide an effective tool for blood donor screening for B. microti in a format amenable to high-throughput and cost-effective screening.

A prospective evaluation of chronic Babesia microti infection in seroreactive blood donors

BACKGROUND

Babesia microti is the foremost infectious risk to the US blood supply for which a Food and Drug Administration (FDA)-licensed test is unavailable for donation screening. Characterization of the antibody response to B. microti and correlation with parasitemia is necessary to guide screening and donor management policies.

STUDY DESIGN AND METHODS

During an FDA licensure trial, blood donors were prospectively screened (July-November 2013) using a B. microti-specific antibody enzyme immunoassay (EIA, Immunetics) in highly endemic (New York [NY]; n = 13,688), moderately endemic (Minnesota [MN]; n = 4583), and nonendemic (New Mexico [NM]; n = 8451) regions. Blood donors with repeat-reactive (RR) results participated in a 12-month prospective cohort study using B. microti EIA, immunofluorescent assay, polymerase chain reaction (PCR), blood smear, and clinical questionnaire.

RESULTS

Thirty-seven (61.67%; 24 NY, seven MN, six NM) of 60 eligible RR donors enrolled in the study; 20 of 37 (54%) completed the 12-month follow-up visit of which 15 (75%) were still seroreactive. Nine PCR-positive donors were identified during index screening; five participated in the follow-up study, three were PCR positive at 6 months, and two remained positive at final follow-up (378 and 404 days). Most RR donors displayed low-level seroreactivity that was either stable or waning during follow-up. The level and pattern of reactivity correlated poorly with PCR positivity.

CONCLUSION

The findings indicate prolonged seropositivity in blood donors. Although rare, asymptomatic, persistent PCR positivity supports the current policy of indefinite deferral for donors with a history of babesiosis or positive test results. Repeat testing by PCR and serology will be necessary if reinstatement is to be considered.

Experimental transfusion-induced Babesia microti infection: dynamics of parasitemia and immune responses in a rhesus macaque model

BACKGROUND

Babesiosis is an emerging tick-borne infection in humans. The increasing numbers of reported cases of transfusion-associated babesiosis (TAB), primarily caused by Babesia microti, represents a concern for the safety of the US blood supply.

STUDY DESIGN AND METHODS

This study investigated kinetics of parasitemia and innate immune responses and dynamics of antibody responses during B. microti infection in rhesus macaques (RMs) using blood smears, quantitative polymerase chain reaction (qPCR), flow cytometry, and indirect fluorescent antibody testing. A total of six monkeys were transfused with either hamster or monkey-passaged B. microti-infected red blood cells (two and four monkeys, respectively) simulating TAB.

RESULTS

The prepatent period in monkeys inoculated with hamster-passaged B. microti was 35 days compared with 4 days in monkeys transfused with monkey-passaged B. microti; the latter monkeys also had markedly higher parasitemia levels. The duration of the window period from the first detected parasitemia by qPCR analysis to the first detected antibody response ranged from 10 to 17 days. Antibody responses fluctuated during the course of the infection. Innate responses assessed by the frequencies of monocytes and activated B cells correlated with the kinetics and magnitude of parasitemia. On Day 14, additional activation peaks were noted for CD14+CD16+ and CD14-CD16+ monocytes and for CD11c+ myeloid dendritic cells, but only in animals transfused with monkey-passaged B. microti. Parasitemia persisted in these immunocompetent animals, similar to human infection.

CONCLUSION

The results suggest that transfusion-associated transmission of B. microti leads to rapid onset of parasitemia (Day 4) in RMs, detectable antibody response 14 days later, and persistent parasitemia.

Seroprevalence of Babesia microti infection in Canadian blood donors

BACKGROUND

Human babesiosis, caused by the intraerythrocytic protozoan parasite Babesia microti, is primarily transmitted by tick bites and is also transmitted by transfusion. Infections have been identified in U.S. blood donors close to Canadian borders. We aimed to assess the risk of transfusion-transmitted babesiosis in Canada by examining infections in ticks and seroprevalence in blood donors.

STUDY DESIGN AND METHODS

Passive surveillance (receipt of ticks submitted by the public) was used to identify regions for tick drag sampling (active surveillance, 2009-2014). All ticks were tested for B. microti using an indirect immunofluorescent antibody assay (Imugen, Inc.). Between July and December 2013, blood donations from selected sites (southern Manitoba, Ontario, Québec, New Brunswick, and Nova Scotia) near endemic U.S. regions were tested for antibody to B. microti. Donors completed a questionnaire about risk travel and possible tick exposure.

RESULTS

Of approximately 12,000 ticks submitted, 14 were B. microti positive (10 in Manitoba, one in Ontario, one in Québec, two in New Brunswick). From active tick surveillance, six of 361 ticks in Manitoba were positive (1.7%), three of 641 (0.5%) in Québec, and none elsewhere. There were 26,260 donors at the selected sites of whom 13,993 (53%) were tested. None were positive for antibody to B. microti. In 2013, 47% of donors visited forested areas in Canada, and 41% traveled to the United States.

CONCLUSION

The data do not suggest that laboratory-based testing is warranted at this time. However, there are indicators that B. microti may be advancing into Canada and ongoing monitoring of tick populations and donor seroprevalence is indicated.

Emerging microbial threats to the United States blood supply

PURPOSE OF REVIEW

In this short review, several emerging agents are described to demonstrate potential responses of the blood community to emerging and potentially emerging infections.

RECENT FINDINGS

Critical questions are raised as we consider appropriate approaches to these agents. Can we identify risk thresholds below which interventions are not required, that is, are there tolerable infectious risks of transfusion? Who are the stakeholders responsible for that determination? What is the role of health economic analysis for informing those decisions? If we decide that cost-utility thresholds for transfusion medicine are appropriately several fold higher than for the rest of clinical medicine, who has responsibility for being certain whether those priorities are funded?

SUMMARY

Four agents will be discussed to highlight the evolving considerations in response to these considerations.

Risks associated with red blood cell transfusions: potential benefits from application of pathogen inactivation

BACKGROUND

Red blood cell (RBC) transfusion risks could be reduced if a robust technology for pathogen inactivation of RBC (PI-RBCs) were to be approved.

MATERIALS AND METHODS

Estimates of per-unit and per-patient aggregate infectious risks for conventional RBCs were calculated; the latter used patient diagnosis as a determinant of estimated lifetime exposure to RBC units. Existing in vitro data for the two technologies under development for producing PI-RBCs and the status of current clinical trials are reviewed.

RESULTS

Minimum and maximum per-unit risk were calculated as 0.0003% (1 in 323,000) and 0.12% (1 in 831), respectively. The minimum estimate is for known lower-risk pathogens while the maximal estimate also includes an emerging infectious agent (EIA) and endemic area Babesia risk. Minimum and maximum per-patient lifetime risks by diagnosis grouping were estimated as 1.5 and 3.3%, respectively, for stem cell transplantation (which includes additional risk for cytomegalovirus transmission); 1.2 and 3.7%, respectively, for myelodysplastic syndrome; and 0.2 and 44%, respectively, for hemoglobinopathy.

DISCUSSION

There is potential for PI technologies to reduce infectious RBC risk and to provide additional benefits (e.g., prevention of transfusion-associated graft-versus-host disease and possible reduction of alloimmunization) due to white blood cell inactivation. PI-RBCs should be viewed in the context of having a fully PI-treated blood supply, enabling a blood safety paradigm shift from reactive to proactive. Providing insurance against new EIAs. Further, when approved, the use of PI for all components may catalyze operational changes in blood donor screening, laboratory testing, and component manufacturing.